Sol is the personification of the Sun and a god in ancient Roman religion. It was long thought that Rome actually had two different, consecutive sun gods. The first, Sol Indiges, was thought to have been unimportant, disappearing altogether at an early period. Only in the late Roman Empire, scholars argued, did solar cult re-appear with the arrival in Rome of the Syrian Sol Invictus, perhaps under the influence of the Mithraic mysteries.[1] Recent publications have challenged the notion of two different sun gods in Rome, pointing to the abundant evidence for the continuity of the cult of Sol, and the lack of any clear differentiation—either in name or depiction—between the "early" and "late" Roman sun god.[2][3][4][5]

According to Roman sources, the worship of Sol was introduced by Titus Tatius shortly after the foundation of Rome[7][8] In Virgil he is the grandfather of Latinus, the son of Sol's daughter Circe who lived not far from Rome at Monte Circeo.[9] A shrine to Sol stood on the banks of the Numicius, near many important shrines of early Latin religion.[10] In Rome Sol had an "old" temple in the Circus Maximus according to Tacitus (AD 56 – 117),[11] and this temple remained important in the first three centuries AD.[12] There was also an old shrine for Sol on the Quirinal, where an annual sacrifice was offered to Sol Indiges on August 9 to commemorate Caesar's victory at Pharsala (48 BC).[13] The Roman ritual calendars or fasti also mention a feast for Sol Indiges on December 11, and a sacrifice for Sol and Luna on August 28. Traditionally, scholars have considered
Sol Indiges ("the native sun" or "the invoked sun"—the etymology and meaning of the word "indiges" is disputed) to represent an earlier, more agrarian form in which the Roman god Sol was worshipped, and considered him to be very different from the late Roman Sol Invictus, whom they believed was a predominantly Syrian deity. Neither the epithet "indiges" (which fell into disuse sometime after Caesar) nor the epithet "invictus" are used with any consistency however, making it impossible to differentiate between the two (see Sol Invictus, see also Di indigetes).

Sol Invictus"Unconquered Sun" was long thought to have been a foreign state-supportedsun god introduced from either Emesa or Palmyra in Syria by the emperor Aurelian in 274 and overshadowing other Eastern cults in importance,[14] until the abolition of Classical Roman religion under Theodosius I. However the evidence for this is meager at best,[15] and the notion that Aurelian introduced a new cult of the sun ignores the abundant evidence on coins, in images, in inscriptions, and in other sources for a strong presence of the sun god in Rome throughout the imperial period.[16]Tertullian (died AD 220) writes that the Circus Maximus was dedicated primarily to Sol.[17] During the reign of Aurelian, a new college of pontiffs for Sol was established.[citation needed]

There is some debate over the significance of the date December 21 for the cult of Sol. According to a single, late source, the Romans held a festival on December 21 of Dies Natalis Invicti, "the birthday of the unconquered one." Most scholars assume Sol Invictus was meant, although our source for this festival does not state so explicitly.[18] December 25 was commonly indicated as the date of the winter solstice,[19] with the first detectable lengthening of daylight hours.
There were also festivals on other days in December, including the 11th (mentioned above), as well as August. Gordon points out that none of these other festivals are linked to astronomical events.[20] When the festival on December 25 was instituted is not clear, which makes it hard to assess what impact (if any) it had on the establishment of Christmas.

The official status of the cult of Sol after Aurelian was significant, but there is no evidence that it was the supreme cult of the state. Hoey exaggerates the importance of an inscription from Salsovia that supposedly indicates an official empire-wide cult-prescription for Sol on December 19.ref"An inscription of unique interest from the reign of Licinius embodies the official prescription for the annual celebration by his army of a festival of Sol Invictus on December 19" (Hoey 1939:480 and note 128).</ref> It actually simply states that at the command of the emperor Licinius the commanding officer of the detachment at Salsovia was to burn incense annually for a newly erected statue of Sol on November 18 (Hoey misread the date).[21] This simply means that Licinius accepted the erection of the statue in his honour.

The Greek assimilation of Apollo and Helios was already established in Rome by the end of the republic.[23] Various Roman philosophers speculated on the nature of the sun, without arriving at any consensus. A typical example is Nigidius, a scholar of the 1st century BC. His works have not survived, but writing five centuries later, Macrobius reports that Nigidius argued that Sol was to be identified with Janus and that he had a counterpart, Jana, who was Luna. As such, they were to be regarded as the highest of the gods, receiving their sacrifices before all the others.[24] Such views appear to have been restricted to an erudite elite—no ancient source aside from Macrobius mentions the equation of Sol with Janus—and had no impact on the well-attested cult of Sol as independent deity.

^A typical example of this line of thought can be found in: Allan S. Hoey, "Official Policy towards Oriental Cults in the Roman Army" Transactions and Proceedings of the American Philological Association,70, (1939:456-481) p 479f.

^Inscription nr. 5 in Inscriptiones Scythiae Minoris Graecae et Latinae 2, Bucharest 1980. The prescription is for "die XIV Kal(endis) Decemb(ribus)" i.e. the 14th day before the kalends of December which is November 18th.